<!DOCTYPE html>
<style>
#container div {
  height: 50px;
  border: 1px solid black;
  margin-top: 2px;
}
#container {
  border: 1px solid green;
  height: 500px;
}
#container #first {
  margin-top: 100px;
  background: yellow;
}
</style>
<div id="container">
  <div id="first"></div>
  <div></div>
  <div style="height: 51px"></div>
  <div></div>
  <div></div>
  <div></div>
  <div></div>
</div>
